Hot melt adhesives, which are generally applied while in the molten or liquid state are, solid at room temperature. Typically, these adhesives are provided in the form of blocks and because of the nature of these materials, particularly the pressure sensitive hot melts, there are problems associated with handling and packaging them. The solid adhesive blocks not only stick or adhere to hands or mechanical handling devices but also to each other. They also pick up dirt and other contaminants. Additionally, certain applications which require high tack formulations result in blocks that will deform or cold flow unless supported during shipment.
The need and advantages for providing tackless or non-blocking hot melt adhesives are apparent and various ways of accomplishing this have been developed. While most of these prior art methods have provided some degree of improvement in the packaging and handling of hot melt adhesives, they have suffered by virtue of either the need to unwrap or otherwise unpackage the hot melt or, in the cases of coated hot melts which are added directly to the melting pots, by virtue of the contamination resulting from the build-up over time of large quantities of the packaging materials in the melt pot and application equipment.
Commonly assigned U.S. Pat. No. 5,373,682 significantly improved upon the state of the art by providing a packaging system and method for packaging hot melt adhesives wherein the hot melt adhesive is pumped or pored into a tube of plastic film in contact with a heat sink. When the hot melt adhesive is poured in its molten state into the plastic packaging film and then allowed to solidify, the adhesive fuses to some extent into the film, resulting in a non-blocking adhesive package which will melt faster in the melt pot and will not cause a build up of undesirable plastic residue even after extended periods of time. The intermingling of one or more of the hot melt components into the contact surface of the plastic film allows some mixing or compatibilizing of the film and the hot melt thereby improving the opportunity for more complete mixing of the hot melt and film when remelting of the packaged hot melt occurs. Such a method also provides an additional benefit over prior non-blocking packages in that the package itself is air-tight allowing no air to be entrapped therein. The presence of entrapped air has been blamed for a variety of problems including incomplete melting and blending of the packaging material into the adhesive whereby the packaging material floats on the surface of the hot melt and/or adheres to the walls of the melt pot. The resultant adhesive package provides a readily handable adhesive in cartridge form that may, advantageously, be produced in a continuous line operation.
Commonly assigned published International Application No. WO 02/061009 A2 advanced the state of the art by providing a system for the packaging of low temperature adhesives and pressure sensitive adhesives, i.e., adhesives formulated for application at temperatures below about 275° F. and down to about 150° F.
Notwithstanding the prior art packaging systems, there continues to be a need for improvements and modification of such packaging systems leading to the wider applicability thereof. The current invention provides such an improvement.